This invention relates to a laser surgical unit for converging a laser beam onto a diseased part of a living tissue in an organism, such as a human body, to perform a surgical operation.
A laser surgical unit of the type described has been used in a surgical operation to remove a diseased part by a laser beam emitted therefrom. More specifically, when the laser beam is irradiated onto the diseased part of a living tissue, beam absorption, temperature elevation, vaporization, incision, coagulation, and hemostasis successively take place in the living tissue. On the beam absorption in the living tissue, the laser beam is transformed into thermal energy. The thermal energy heats water in the living tissue to cause vaporization to occur. In this event, a surface of the living tissue is heated to a high temperature at which the coagulation layer is formed. Due to the vaporization, the surface of the living tissue is expanded and ruptured to thereby perform incision of the living tissue. The coagulation layer serves to perform hemostasis.
Such laser surgical units are classified into contact and non-contact laser surgical units which comprise contact and non-contact laser probes, respectively.
As contact and noncontact laser surgical units, use has been made either for a CO.sub.2 (carbon dioxide gas) laser surgical unit which comprises a non-contact laser probe or for a Nd (neodymium) laser surgical unit which comprises a contact laser probe.
Specifically, the CO.sub.2 laser surgical unit generates a laser beam at an oscillation wavelength of 10 .mu.m. Such a laser beam is highly absorbed in a hydroxyl group (OH) which is rich in a living tissue. This is because the non-contact laser probe is included in the CO.sub.2 laser surgical unit to emit the laser beam onto the living tissue and to cause the laser beam to be directly absorbed in the living tissue. Consequently, the living tissue itself is heated to cause vaporization to occur in the living tissue. Thus, incision is performed.
On the other hand, the Nd laser surgical unit generates a laser beam at an oscillation wavelength of 1 .mu.m. Such a laser beam is low in absorption in the living tissue. If a high absorption material for the laser beam, for example manganese dioxide, is coated on the entire surface of the contact laser probe so as to absorb the laser beam, the tip of the contact laser probe itself is heated. For example, such an Nd laser surgical unit is disclosed in Japanese Patent Prepublication No. 318934/1988. Incision and hemostasis are performed with the probe heated to a high temperature.
The CO.sub.2 laser surgical unit mentioned above provides a beautiful cut surface because the CO.sub.2 laser surgical unit generates the laser beam highly absorbed in the living tissue. However, most of the energy of the laser beam is consumed in vaporization because of its high absorptivity in the living tissue. Therefore, the living tissue is insufficiently heated. As a result, a coagulation layer of a sufficient thickness can not be formed. Thus, the CO.sub.2 laser surgical unit has a degraded hemostatic ability.
Since the CO.sub.2 laser surgical unit is of a non-contact type, a surgeon or an operator can not feel by sense of touch in a surgical operation. It is therefore difficult to perform uniform incision with the laser beam constantly focused along a cutting line.
On the other hand, the Nd laser surgical unit performs incision by the use of a heat generated in the coating film on a tip portion of the contact laser probe. A coagulation layer of an appropriate thickness is formed. Thus, hemostasis and incision are performed. However, the coating film on the tip portion of the contact laser probe is often exfoliated due to heat. If the coating film is exfoliated, the contact laser probe suffers variation in the heat generated at the surface of the contact laser probe. This results in fluctuation of cutting ability of the contact laser probe to unfavorably provide a variable sense of touch felt by the operator. When incision is carried out by the use of such a contact laser probe, the operator may be affected by the variable sense of touch to produce an operation error, for example, in the cutting rate. In the presence of the operation error, the living tissue is overheated to form a nonuniform coagulation layer having a too thick portion or a too deep portion.